Creating curve design
Some technics to do that (I won't make here the exact same bottle...):

Knife cut

The cut is straight, but the result is parabolic due to the bottle shape.



Knife project

Again a curved shape obtained from a flat curve.


Create a cutting shape (here a plane)
Scale/orientate it
Shift select the bottle and enter edit mode in the bottle (both are selected and that indicates to Blender which shape(s) will cut the bottle)
Use 'knife project'
In your situation, make sure that 'cut through' is checked




Beveling


In edge selection mode
Select the wanted edge loops
Use CtrlB
Choose bevel depth with Numpad + and Numpad -


Once done, give a shape, for instance selecting the two face loops as below and scale them:



Draw it flat and bend the shape


Use a mirror to make so the future cutting lines will match
Add a simple deform modifier to bend the shape to 360°
Make the cuts/bevels as previously
Apply the modifiers and remove doubles when the shape is as you want
Add a subsurface modifier
Scale and merge (or extrude and model) the shape to fit your bottle